Outline
The invention relates to the field of assessing transport activity of OATP (Organic anion-transporting polypeptide) and ABC (ATP Binding Cassette) transport proteins. In particular, the invention relates to methods for determining in a single, fluorescence-based assay whether a compound is a modulator of OATP and/or MRP2 (Multidrug resistance associated protein, ABCC) transport activity, using a fluorescent compound that is a substrate of both OATP and MRP2, and is selected from sulfopyrenes having general formula (I) or sulforhodamines having general formula (II).